Sample

public class MyAPI {
  @GET("{path}")
  Call<List<Data>> getData(@Path("path") String pathValue);
}

public class Repo {
  private Context _context;
  private List<Data> _loadedData;
  private MyRetrofitService _retrofitService;
  
  // Not sure you need context!
  public Repo(Context context) {
    _context = context;
    
    // implementation 'com.google.code.gson:gson:2.8.2'
    // implementation 'com.squareup.retrofit2:retrofit:2.3.0'
    // implementation 'com.squareup.retrofit2:converter-gson:2.3.0'
    Retrofit retrofit = new Retrofit.Builder()
      .baseUrl("https://<your base url>")
      .addConverterFactory(GsonConverterFactory.create())
      .build();

    _retrofitService = retrofit.create(MyAPI.class);
  }
  
  public void getData(String input, MyCallback myCallback) {
    if (loadedData != null) { // use local data
      loadData(_loadedData, input, callback);
    } else { // load data from network
      retrofit.getData(new Callback {
        void onResponse(Response response) {
          // Save to local
          _loadedData = _retrofitService.getData();
          
          Call <List<SponsorsResult>> call = service.getData();

          call.enqueue(new Callback<List<Data>>() {
              @Override
                public void onResponse(Call<List<Data>> call, Response<List<Data>> response) {
                List<Data> data = response.body();
                _loadedData = data;
                loadData(_loadedData, input, myCallback);
              }

              @Override
                public void onFailure(Call<List<Data>> call, Throwable t) {
                myCallback.onError("Print t")
              }
        });
    }
  }
  
  private void loadData(List<Data> data, String input, MyCallback myCallback) {
    String parsedInput = parseInput(data, input);
    if (parseInput == null) {
      callback.onError("Invalid input");
    } else {
      String result = fetchResult(data, input);
      callback.onSuccess(parsedInput, result);
    }
  }
  
}